1. Field of the Invention
The present invention relates, in general, to vehicles, and in particular, to a vehicle suspension for a leaning vehicle, i.e., one that leans side-to-side as it turns.
2. Information Disclosure Statement
Motorcycle accidents claim over 5,000 lives per year and over 1,000 lives per year in single-vehicle accidents. Two-wheeled motorized vehicles such as motorcycles have excellent acceleration, efficiency, and cornering prowess, but poor control and stability. Four-wheeled vehicles such as all-terrain vehicles (“ATVs”) have good control and stability but lack the efficiency and cornering ability of motorcycles.
Motorcycles are known to be susceptible to so-called “low-side crashes”, which are caused by loss of front wheel traction during a turn, and which are the most prevalent cause of single-vehicle motorcycle accidents. Motorcycles are also known to be susceptible to so-called “high-side crashes”, which are caused by a sudden increase in rear wheel traction that quickly leans a motorcycle out of a turn, and which are the most violent of single-vehicle motorcycle accidents.
It is therefore desirable to have a safer leaning vehicle suspension that provides a stable high-performance vehicle, that substantially eliminates low-side crashes and high-side crashes common in prior art vehicles, and that combines the high cornering speeds and low vehicle weight of a motorcycle with stability and control heretofore only possible with four-wheeled vehicles.
It is further desirable to have improved front wheel braking performance as compared with prior art two-wheeled motorcycles, and to significantly reduce the danger of front wheel lockup under heavy braking conditions.
It is still further desirable to provide a leaning vehicle suspension that improves safety and permits use with a fuel-efficient vehicle that has high performance while also being inexpensive to construct.
Prior art three-wheeled ATV designs are known that were popular in the late 1980s, subsequently banned as unsafe by the Consumer Product Safety Commission, which had a single steerable front wheel and a pair of rear wheels mounted on a solid rear axle. Such prior art designs are incapable of nimble handling and have poor performance characteristics.
Two principal factors, namely, gyroscopic forces and steering input, are known to affect balance and stability of a two-wheeled vehicle.
Typically, gyroscopic precession forces only contribute significantly to balance at high speed. Greater wheel masses, of course, impart greater stabilizing forces. When riding a motorcycle at high speeds, it can be noted that steering effort becomes “heavy”. The rider experiences a much higher resistance to steering inputs because of the gyroscopic stabilization effect. However, at low speeds this effect is quite minor and not nearly significant enough to generate the forces required to balance a motorcycle. Experimentation with vehicles equipped with counter-rotating wheel weights confirms that two-wheeled vehicle balance and stability remain largely intact even when gyroscopic forces have been canceled.
By far the greatest influence on two-wheeled vehicle balance is steering input. As long as the vehicle and rider's combined center of gravity sits on the line connecting the front and rear, a two-wheeled vehicle is in balance. As anyone who has ever ridden a bicycle through a puddle might notice, tracks left by the front wheel are akin to a sine wave, weaving left and right across the track of the rear wheel. Balance on a two-wheeled vehicle is a series of falls. As described from a rider's perspective, when the bicycle starts to tip to the left, for example, the center of gravity also moves left. Thus, to maintain balance, the rider must steer left so that the front wheel moves left. At some point in this maneuver, the bicycle leans back upright. In a typical case, however, the rider will still have the handlebars turned slightly left, causing the center of gravity to move to the right of the line connecting the front and rear ground contact patches, thereby causing the bicycle to now lean to the right. The rider compensates by steering to the right, and the process repeats. Skilled riders are often so smooth, and their oscillations so minor, that this balance mechanism goes unnoticed. Performance motorcycle riding schools worldwide, however, teach the mantra “push right to go right”. In other words, pushing on the right handlebar (which turns the front wheel to the left) initiates a rightward vehicle lean. This “fall” allows the rider to set a cornering lean angle that is appropriate for the vehicle's speed and intended trajectory. The rider then turns the front wheel back to the right to maintain balance.
The inventors are aware of the following patents and publications, some of which may be relevant to the present invention: Bourne, Jr., U.S. Pat. No. 4,624,469 (issued Nov. 25, 1986); Satoh et al., U.S. Pat. No. 5,005,859 (issued Apr. 9, 1991); Brudeli, U.S. Pat. No. 7,530,419 (issued May 12, 2009); Suhre et al., U.S. Pat. No. 7,591,337 (issued Sep. 22, 2009); Suhre et al., U.S. Patent Application Publication No. US 2007/0075517 A1 (published Apr. 5, 2007); Brudeli, U.S. Patent Application Publication No. US 2007/1076384 A1 (published Aug. 2, 2007); MMT 280897—Tracer Steering Geometry (Dec. 6, 2000) (Millennium Motorcycles, North Fremantle, Australia); MMT 030100—Tracer Steering Hub Honda VT 250 Wheels (Dec. 6, 2000) (Millennium Motorcycles, North Fremantle, Australia); HyperTrike (Dec. 6, 2000) (Millennium Motorcycles, North Fremantle, Australia); Monotracer—Expanding a Sustainable Concept of Driving (Apr. 3, 2008) (Peraves AG, Winterthur, Switzerland); TL1000 Motorcycle Service Manual (1997) (rotary damper shown on pages 6-33, 6-34, 6-35, and 6-36) (Suzuki Motor Corporation, Takatsuka, Japan); YZ250T1 Motorcycle Parts Reference (2005) (rear wheel shown in Drawing 5NY1100-A271) (Yamaha Corporation, Shizuoka, Japan).
None of these references, either singly or in combination, discloses or suggests the present invention.